U.S. patent application number 17/469139 was filed with the patent office on 2022-03-10 for chemically strengthened glass with a film and method for measuring surface stress of chemically strengthened glass.
This patent application is currently assigned to AGC Inc.. The applicant listed for this patent is AGC Inc.. Invention is credited to Seiki OHARA, Hironobu SATO, Shunji WACHI.
Application Number | 20220073425 17/469139 |
Document ID | / |
Family ID | 80470562 |
Filed Date | 2022-03-10 |
United States Patent
Application |
20220073425 |
Kind Code |
A1 |
OHARA; Seiki ; et
al. |
March 10, 2022 |
CHEMICALLY STRENGTHENED GLASS WITH A FILM AND METHOD FOR MEASURING
SURFACE STRESS OF CHEMICALLY STRENGTHENED GLASS
Abstract
The present invention relates to a chemically strengthened glass
with a film, including: a chemically strengthened glass having a
pair of main surfaces opposing each other; and a film formed on at
least one of the main surfaces of the chemically strengthened
glass, in which the chemically strengthened glass has two or less
interference fringes observed under stress measurement utilizing
surface propagation light having a wavelength of 365 nm, and the
film has a refractive index lower than a refractive index of the
chemically strengthened glass.
Inventors: |
OHARA; Seiki; (Tokyo,
JP) ; WACHI; Shunji; (Tokyo, JP) ; SATO;
Hironobu; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AGC Inc. |
Tokyo |
|
JP |
|
|
Assignee: |
AGC Inc.
Tokyo
JP
|
Family ID: |
80470562 |
Appl. No.: |
17/469139 |
Filed: |
September 8, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 3/095 20130101;
C03C 17/32 20130101; C03C 2217/734 20130101; C03C 17/42 20130101;
C03C 2217/732 20130101; C03C 17/28 20130101; G01L 1/24 20130101;
C03C 21/002 20130101; C03C 2218/151 20130101 |
International
Class: |
C03C 21/00 20060101
C03C021/00; C03C 17/32 20060101 C03C017/32; G01L 1/24 20060101
G01L001/24 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 9, 2020 |
JP |
2020-151342 |
Claims
1. A chemically strengthened glass with a film, comprising: a
chemically strengthened glass having a pair of main surfaces
opposing each other; and a film formed on at least one of the main
surfaces of the chemically strengthened glass, wherein the
chemically strengthened glass has two or less interference fringes
observed under stress measurement utilizing surface propagation
light having a wavelength of 365 nm, and the film has a refractive
index lower than a refractive index of the chemically strengthened
glass.
2. The chemically strengthened glass with a film according to claim
1, wherein a difference between the refractive index of the film
and the refractive index of the chemically strengthened glass is in
a range of 0.02 to 0.30.
3. The chemically strengthened glass with a film according to claim
1, wherein a stress depth of a deep layer of the chemically
strengthened glass is 0.1.times.t or more, where t is a thickness
of the chemically strengthened glass.
4. The chemically strengthened glass with a film according to claim
1, wherein the chemically strengthened glass has a base composition
comprising 5 mol % or more of Li.sub.2O in mole percentage on an
oxide basis.
5. The chemically strengthened glass with a film according to claim
1, wherein the film has a thickness in a range of 2 nm to 50
nm.
6. The chemically strengthened glass with a film according to claim
1, wherein the film comprises a fluorine-based organic
compound.
7. A surface stress measuring method for a chemically strengthened
glass having a pair of main surfaces opposing each other, the
method comprising: obtaining a chemically strengthened glass with a
film by forming a film having a refractive index lower than a
refractive index of the chemically strengthened glass on at least
one of the main surfaces of the chemically strengthened glass; and
measuring a surface compressive stress of the chemically
strengthened glass by performing stress measurement utilizing
surface propagation light on the chemically strengthened glass with
a film, wherein the chemically strengthened glass has two or less
interference fringes observed under stress measurement utilizing
surface propagation light having a wavelength of 365 nm.
8. The surface stress measuring method for a chemically
strengthened glass according to claim 7, wherein the surface
propagation light to be applied to the chemically strengthened
glass with a film has a wavelength of 650 nm or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to chemically strengthened
glass with a film and a method for measuring surface stress of
chemically strengthened glass.
BACKGROUND ART
[0002] Chemically strengthened glass is used as cover glasses of
electronic devices such as portable terminals.
[0003] Chemically strengthened glass is glass in which a
compressive stress layer is formed in a surface layer of the glass
by, for example, bringing glass into contact with molten salt
containing alkali metal ions and thereby causing ion exchange
between alkali metal ions in the glass and alkali metal ions in the
molten salt. The strength of chemically strengthened glass thus
obtained strongly depends on its stress profile.
[0004] The cover glass of a portable terminal or the like may be
broken due to deformation that occurs when, for example, the
terminal is dropped. To prevent such breaking, that is,
bending-mode braking, it is effective to increase the compressive
stress at the glass surface.
[0005] There may also occur a case that the cover glass of a
portable terminal or the like is broken due to collision with a
projection when is dropped onto an asphalt surface or sand. To
prevent such breaking, that is, impact-mode braking, it is
effective to increase the depth of a compressive stress layer to
form a compressive stress layer to a deeper portion of glass.
[0006] More specifically, the probability of occurrence of
bending-mode braking can be suppressed by producing large
compressive stress in a surface portion of glass by sodium
ion-potassium ion exchange. The probability of occurrence of
impact-mode braking can also be suppressed by further producing a
little small compressive stress in a deeper portion of the glass by
lithium ion-sodium ion exchange.
[0007] However, when a compressive stress layer is formed in a
surface portion of glass, tensile stress corresponding to the
surface compressive stress is necessarily produced in a central
portion of the glass. If the tensile stress is too large, when the
glass is broken the breaking tends to be so violent that fragments
are scattered.
[0008] It is desired to prevent glass from being broken so
violently that fragments are scattered while suppressing the
probabilities of occurrence of both of bending-mode braking and
impact-mode braking. For such purpose, it is conceivable to
increase the compressive stress at the glass surface and form a
compressive stress layer to a deeper portion and, at the same time,
make the depth of compressive stress produced in a glass surface
portion by sodium ion-potassium ion exchange smaller.
[0009] Patent document 1 discloses, as chemically strengthened
glass that is high in strength and low in the degree of scattering
of fragments, chemically strengthened glass produced by two-step
ion exchange treatment.
CITATION LIST
Patent Literature
[0010] [Patent document 1] U.S. Pat. No. 9,487,434 [0011] [Patent
document 2] JP-B-559-37451 [0012] [Patent document 3] Japanese
Patent No. 6,713,651
Technical Problems
[0013] In general, stress in a region, in which sodium ions have
been replaced by potassium ions, in a glass surface layer is
determined from interference fringes obtained utilizing light that
propagates through the glass surface layer, that is, surface
propagation light (refer to Patent document 2). However, it has
been found that interference fringes become unclear if the depth of
compressive stress produced by potassium ions in a glass surface
portion is made extremely smaller than before.
[0014] The number of interference fringes observed can be increased
by making the wavelength of surface propagation light shorter.
However, even when light having a wavelength of 365 nm is used,
there may occur a case that the number of interference fringes
observed is two or less. Particularly when the number of
interference fringes observed is two or less, the fringes are
unclear and hence it is very difficult to determine compressive
stress at the glass surface.
SUMMARY OF INVENTION
[0015] In view of the above, an object of the present invention is
to provide a new method for measuring surface stress of chemically
strengthened glass for which measurement of compressive stress at
the surface is very difficult or impossible because interference
fringes observed utilizing surface propagation light are unclear,
as well as chemically strengthened glass with a film that enables
such measurement.
[0016] Making diligent studies, the present inventors have found
that the above problems can be solved by forming a film that is
lower in refractive index than chemically strengthened glass on a
main surface of the chemically strengthened glass. This is opposite
to the conventional knowledge that to perform measurement utilizing
surface propagation light an immersion liquid that is equivalent to
or higher than target glass in refractive index should be applied
to the glass surface. This will be described below in a specific
manner.
[0017] Where chemically strengthened glass is used in a display
unit of an electronic device such as a cellphone or a smartphone, a
film may be formed on a main surface of the chemically strengthened
glass to provide an antiglare effect, an antibacterial effect, an
antifouling effect, or the like. Such a film is lower in refractive
index than the chemically strengthened glass.
[0018] It was thought conventionally that when an antiglare film,
an antibacterial film, an antifouling film, or the like is formed
on the chemically strengthened glass for these purposes,
observation of interference fringes produced by surface propagation
light would be more difficult than a case of chemically
strengthened glass on which a film is not formed (refer to Patent
document 3).
[0019] The present inventors have found that in a case where
interference fringes obtained utilizing surface propagation light
are unclear because the depth of compressive stress produced by
potassium ions in a surface of chemically strengthened glass is
very small, formation of a low refractive index film rather
increases the clearness of interference fringes contrary to the
above knowledge.
[0020] The present invention provides the followings:
[0021] [1] A chemically strengthened glass with a film,
including:
[0022] a chemically strengthened glass having a pair of main
surfaces opposing each other; and
[0023] a film formed on at least one of the main surfaces of the
chemically strengthened glass,
[0024] in which the chemically strengthened glass has two or less
interference fringes observed under stress measurement utilizing
surface propagation light having a wavelength of 365 nm, and
[0025] the film has a refractive index lower than a refractive
index of the chemically strengthened glass.
[0026] [2] The chemically strengthened glass with a film according
to item [1], in which a difference between the refractive index of
the film and the refractive index of the chemically strengthened
glass is in a range of 0.02 to 0.30.
[0027] [3] The chemically strengthened glass with a film according
to item [1] or [2], in which a stress depth of a deep layer of the
chemically strengthened glass is 0.1.times.t or more, where t is a
thickness of the chemically strengthened glass.
[0028] [4] The chemically strengthened glass with a film according
to any one of items [1] to [3], in which the chemically
strengthened glass has a base composition including 5 mol % or more
of Li.sub.2O in mole percentage on an oxide basis.
[0029] [5] The chemically strengthened glass with a film according
to any one of items [1] to [4], in which the film has a thickness
in a range of 2 nm to 50 nm.
[0030] [6] The chemically strengthened glass with a film according
to any one of items [1] to [5], in which the film includes a
fluorine-based organic compound.
[0031] [7] A surface stress measuring method for a chemically
strengthened glass having a pair of main surfaces opposing each
other, the method including:
[0032] obtaining a chemically strengthened glass with a film by
forming a film having a refractive index lower than a refractive
index of the chemically strengthened glass on at least one of the
main surfaces of the chemically strengthened glass; and measuring a
surface compressive stress of the chemically strengthened glass by
performing stress measurement utilizing surface propagation light
on the chemically strengthened glass with a film, in which the
chemically strengthened glass has two or less interference fringes
observed under stress measurement utilizing surface propagation
light having a wavelength of 365 nm.
[0033] [8] The surface stress measuring method for chemically
strengthened glass according to item [7], in which the surface
propagation light to be applied to the chemically strengthened
glass with a film has a wavelength of 650 nm or less.
[0034] The present invention can provide chemically strengthened
glass that makes it possible to measure compressive stress at the
glass surface utilizing surface propagation light even if the depth
of compressive stress produced by potassium ions in a surface
portion is very small. The present invention can also provide a new
surface stress measuring method for such chemically strengthened
glass.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 shows an image of interference fringes obtained by
performing measurement on chemically strengthened glass of Example
1 using a surface stress meter.
[0036] FIG. 2 shows an image of interference fringes obtained by
performing measurement on chemically strengthened glass of Example
2 using a surface stress meter.
[0037] FIG. 3 shows an image of interference fringes obtained by
performing measurement on chemically strengthened glass with a film
of Example 3 using a surface stress meter.
[0038] FIG. 4 shows an image of interference fringes obtained by
performing measurement on chemically strengthened glass with a film
of Example 4 using a surface stress meter.
[0039] FIG. 5 shows an image of interference fringes obtained by
performing measurement on chemically strengthened glass with a film
of Example 5 using a surface stress meter.
DETAILED DESCRIPTION OF EMBODIMENT
[0040] <Chemically Strengthened Glass with Film>
[0041] A chemically strengthened glass with a film of an embodiment
includes a chemically strengthened glass having a pair of main
surfaces opposing each other and a film formed on at least one of
the main surfaces. The chemically strengthened glass has two or
less interference fringes observed under stress measurement
utilizing surface propagation light having a wavelength of 365 nm.
The film formed on at least one of the main surfaces of the
chemically strengthened glass has a refractive index lower than a
refractive index of the chemically strengthened glass.
[0042] The chemically strengthened glass has two or less
interference fringes observed under stress measurement utilizing
surface propagation light having a wavelength of 365 nm. In this
description, the feature that the number of interference fringes is
two or less means that no interference fringe is observed or the
number of interference fringes observed is one or two.
[0043] Surface compressive stress and its depth are calculated from
an interval of observed interference fringes. If the number of
interference fringes is three or more, the amount of information is
large, whereby the accuracy of surface compressive stress and its
depth calculated is high. On the other hand, if the number of
interference fringes is two or less, the interference fringes are
prone to be unclear and hence it is difficult to calculate surface
compressive stress and its depth. Example wavelengths of surface
propagation light used for stress measurement are 790 nm, 596 nm,
365 nm, etc., and observed interference fringes become clearer and
increased in number as the wavelength becomes shorter. In this
specification, the expression "interference fringes are unclear"
means that observed interference fringes are so unclear that
surface compressive stress cannot be determined automatically by
detecting positions and an inclination angle of the interference
fringes when stress measurement is performed using surface
propagation light having a wavelength of 365 nm.
[0044] However, where the depth of compressive stress produced by
potassium ions in a surface portion of chemically strengthened
glass is extremely small, interference fringes are unclear and the
number thereof become two or less even if surface propagation light
having a wavelength of 365 nm is used. In this case, surface
compressive stress and its depth cannot be determined properly.
[0045] The reason why interference fringes are unclear when the
depth of compressive stress produced by potassium ions is extremely
small are inferred as follows.
[0046] The stress measurement utilizing surface propagation light
is a method of measuring stress using interference fringes of light
propagating through a high refractive index region, produced by
replacement of sodium ions with potassium ions, of a glass surface.
It is therefore considered that if a region where light can
propagate is narrow, propagation light expands to make interference
fringes unclear. This can be explained by referring to a phenomenon
of an optical fiber where light propagates through the core having
a high refractive index as the similar case.
[0047] There are following two factors in increasing the beam
diameter in an optical fiber:
[0048] (i) The core diameter which determines a light propagation
region is small, that is, a region having a high refractive index
is narrow.
[0049] (ii) The difference between the refractive indices of the
core and the cladding is small.
[0050] The following two factors in making interference fringes
wider and unclear are obtained by applying the above two factors to
stress measurement utilizing surface propagation light:
[0051] (i') The stress layer to serve as a light propagation region
is shallow.
[0052] (ii') The surface compressive stress is small.
[0053] That is, it is considered that if the compressive stress
produced by potassium ions introduced by ion exchange, that is, the
surface compressive stress of the glass is small and its depth is
small, the light propagation region becomes narrow and propagation
light expands, whereby interference fringes become unclear.
[0054] If a film (hereinafter also referred to as "low refractive
index film") that is lower in refractive index than such chemically
strengthened glass is formed on at least one of its main surfaces,
when stress measurement is performed utilizing surface propagation
light having a wavelength of 365 nm, resulting interference fringes
become clear even if the number thereof is only two, enabling
automatic measurement of surface compressive stress.
[0055] This phenomenon is opposite to the conventional knowledge
that if an antiglare film, an antibacterial film, an antifouling
film, or the like that is lower in refractive index than chemically
strengthened glass is formed on its main surface, observation of
interference fringes produced by surface propagation light would
become more difficult than in a case of chemically strengthened
glass on which no such film is formed.
[0056] This is considered due to the fact that when the depth of
surface compressive stress of chemically strengthened glass is very
small the region where the refractive index is changed by chemical
strengthening is small.
[0057] That is, it is inferred that in contrast to fact that the
refractive index variation region is small and propagation light
expands in the case where the depth of surface compressive stress
is very small, the expansion of propagation light can be suppressed
by forming a low refractive index film.
[0058] The advantage that the presence of a low refractive index
film enables observation of clear interference fringes can be
obtained irrespective of the kind and the number of low refractive
index films and presence of another layer.
[0059] More specifically, either only one kind of low refractive
index film or two or more kinds of low refractive index films may
be formed and only one kind of low refractive index film may be
formed in the form of plural layers. Furthermore, a low refractive
index film may be formed directly on a main surface of chemically
strengthened glass or another layer may be formed between
chemically strengthened glass and a low refractive index film. The
other layer may be a film (hereinafter may be referred to as a
"high refractive index film") that is higher in refractive index
than the chemically strengthened glass.
[0060] The low refractive index film is formed on at least one of
the main surfaces of the chemically strengthened glass and may be
formed on both main surfaces.
[0061] The advantage that interference fringes of chemically
strengthened glass with a film become clear is due to the
refractive index distribution. It is therefore preferable that
chemically strengthened glass and a film(s) be arranged in order of
chemically strengthened glass-low refractive index film, glass-low
refractive index film-high refractive index film, glass-high
refractive index film-low refractive index film, glass-high
refractive index film-low refractive index film-high refractive
index film, or the like.
[0062] From the viewpoint of suppressing expansion of propagation
light, it is preferable that the difference (n.sub.g-n.sub.m)
between the refractive index n.sub.g of the chemically strengthened
glass and the refractive index nm of the low refractive index film
be 0.02 or more, even preferably 0.03 or more, further preferably
0.05 or more, and even further preferably 0.07 or more. On the
other hand, from the viewpoint of preventing a phenomenon that
stress measurement using a surface stress meter is made difficult
due to total reflection at the interface between the chemically
strengthened glass and the low refractive index film, it is
preferable that the refractive index difference (n.sub.g-n.sub.m)
be 0.30 or less, even preferably 0.25 or less, further preferably
0.20 or less, and even further preferably 0.15 or less.
[0063] A refractive index n.sub.g of chemically strengthened glass
and a refractive index nm of a low refractive index film are
measured by a refractive index meter.
(Chemically Strengthened Glass)
[0064] There are no particular limitations on the glass to be
subjected to chemically strengthening treatment as long as
chemically strengthening treatment can be performed on it; for
example, it is preferable that the glass to be subjected to
chemically strengthening treatment contain alkali metals having
small ion radii such as lithium and sodium. Examples of such glass
are aluminosilicate glass, soda-lime silicate glass, borosilicate
glass, lead glass, alkali barium glass, and alumino-borosilicate
glass.
[0065] In this specification, glass that has been subjected to
chemically strengthening treatment is referred to as "chemically
strengthened glass." The base composition of chemically
strengthened glass is the same as the composition of the glass that
have not been subjected to the chemically strengthening treatment
yet. The term "base composition of chemically strengthened glass"
means the composition of the inside of the glass that does not
include a layer that has been subjected to ion exchange by the
chemically strengthening treatment.
[0066] The range of surface stress depth at which the number of
observed interference fringes is two or less is not determined
uniquely because it varies depending on the base composition, the
surface compressive stress, and the depth of diffused potassium
ions of chemically strengthened glass.
[0067] However, for example, the surface stress depth at which the
number of observed interference fringes is two or less is
approximately 4 .mu.m or less in a case where common glass
containing alkali ions has been subjected to chemically
strengthening treatment. Although there are no particular
limitations on the lower limit of the surface stress depth, the
surface stress depth is, for example, 1.8 .mu.m or more.
[0068] For example, the surface compressive stress at which the
number of observed interference fringes is two or less is
approximately 1,200 MPa or less in a case where common glass
containing alkali ions has been subjected to chemically
strengthening treatment. Although there are no particular
limitations on the lower limit of the surface compressive stress,
in view of the use as a cover glass, it is preferable that the
surface compressive stress be 400 MPa or more, even preferably 550
MPa or more and further preferably 700 MPa or more.
[0069] Values of the above-mentioned surface compressive stress and
surface stress depth are determined by a surface stress meter
utilizing surface propagation light, that is, a light guiding
surface stress meter. A deep layer stress depth (described later)
of chemically strengthened glass is determined by a scattered light
photoelastic stress meter.
[0070] Although a light guiding surface stress meter can measure
stress correctly in a short time, it can measure stress only in a
case that the refractive index decreases from the surface toward
the inside of a sample. Thus, it is suitable for measurement of
surface compressive stress of chemically strengthened glass in
which sodium ions have been replaced by potassium ions by ion
exchange. A specific example of the light guiding surface stress
meter is "FSM-6000" produced by Orihara Industrial Co., Ltd.
[0071] Although a scattered light photoelastic stress meter can
measure stress irrespective of the refractive index distribution,
it is prone to be influenced by surface scattering and hence
sometimes cannot measure stress in vicinity of the surface
correctly. Thus, it is suitable for measurement of stress in a deep
layer, in which lithium ions have been replaced by sodium ions by
ion exchange, of chemically strengthened glass. A specific example
of the scattered light photoelastic stress meter is "SLP2000"
produced by Orihara Industrial Co., Ltd.
[0072] That is, a correct stress profile can be obtained by
combining a light guiding surface stress meter and a scattered
light photoelastic stress meter.
[0073] There are no particular limitations on the refractive index
n.sub.g of the chemically strengthened glass as long as it is
higher than that of the low refractive index film. From the
viewpoint of preventing a situation that measurement of stress by a
surface stress meter is difficult because of total reflection at
the boundary between the chemically strengthened glass and the low
refractive index film, it is preferable that the refractive index
n.sub.g be 1.30 or more, even preferably 1.35 or more and further
preferably 1.40 or more. From the viewpoint of suppressing
expansion of propagation light, it is preferable that the
refractive index n.sub.g be 1.54 or less, even preferably 1.52 or
less, further preferably 1.50 or less, and even further preferably
1.48 or less.
[0074] As a large compressive stress is produced in the chemically
strengthened glass due to ion exchange of sodium ions in a surface
portion and potassium ions, it is preferable that its base
composition includes Na.sub.2O. It is preferable that the content
of Na.sub.2O be 2 mol % or more, even preferably 3 mol % or more,
further preferably 4 mol % or more, and even further preferably 5
mol % or more. There are no particular limitations on the upper
limit of the content of Na.sub.2O. From the viewpoint of increasing
the stress in a glass deep portion, it is preferable that the
content of Na.sub.2O be 12 mol % or less, even preferably 10 mol %
or less and further preferably 8 mol % or less. In this
specification, the base composition of the chemically strengthened
glass is expressed in mole percentage on an oxide basis unless
otherwise specified.
[0075] It is preferable that the surface compressive stress and the
surface stress depth be in the above-mentioned preferable ranges as
a result of ion exchange with potassium ions.
[0076] As a little small compressive stress is produced in a deeper
portion of the chemically strengthened glass by ion exchange
between lithium ions and sodium ions, it is preferable that the
base composition of the chemically strengthened glass includes
Li.sub.2O. It is preferable that the content of Li.sub.2O be 5 mol
% or more, even preferably 6 mol % or more and further preferably 8
mol % or more. There are no particular limitations on the upper
limit of the content of Li.sub.2O. From the viewpoint of preventing
devitrification at the time of glass forming, it is preferable that
the content of Li.sub.2O be 14 mol % or less, even preferably 12
mol % or less and further preferably 11 mol % or less.
[0077] A region that is deeper than a surface portion where
compressive stress is produced by potassium ions and in which a
compressive stress layer is formed by sodium ions is referred to as
a "deep layer" of the chemically strengthened glass.
[0078] From the viewpoint of increasing the strength at the time of
dropping, it is preferable that the stress depth of the deep layer
of the chemically strengthened glass be (0.01.times.t) or more,
even preferably (0.012.times.t) or more, further preferably
(0.1.times.t) or more, even further preferably (0.12.times.t) or
more, and particularly preferably (0.15.times.t) or more, where t
is the thickness of the chemically strengthened glass. From the
viewpoint of preventing the glass from breaking to pieces, it is
preferable that the stress depth of the deep layer be
(0.25.times.t) or less, even preferably (0.23.times.t) or less and
further preferably (0.21.times.t) or less.
[0079] A stress depth of the deep layer of the chemically
strengthened glass can be measured by a scattered light
photoelastic stress meter.
[0080] There are no particular limitations on the thickness t of
the chemically strengthened glass. However, where the chemically
strengthened glass is used as a cover glass of a mobile device, it
is preferable that the thickness t be 0.1 mm or more, even
preferably 0.2 mm or more and further preferable 0.5 mm or more.
And it is preferable that the thickness t be 2.5 mm or less, even
preferably 1.5 mm or less and further preferably 1 mm or less.
Where the chemically strengthened glass is used for an image
display device such as a display device, a car navigation device, a
console panel, or an instrument panel, it is preferable that the
thickness t be 0.1 mm or more, even preferably 0.2 mm or more and
further preferably 0.5 mm or more. And it is preferable that the
thickness t be 2.1 mm or less, even preferably 1.8 mm or less and
further preferably 1.5 mm or less.
[0081] If the chemically strengthened glass has, for example, a
specific base composition described below, it is easy to form a
preferable stress profile by chemically strengthening
treatment.
[0082] In mole percentage on an oxide basis, it is preferable that
SiO.sub.2 be contained at 50-80%, Al.sub.2O.sub.3 at 8-20%,
B.sub.2O.sub.3 at 0-10%, Li.sub.2O at 5-14%, and Na.sub.2O at
2-12%, K.sub.2O at 0-10% and that the total content
(MgO+CaO+SrO+BaO) of MgO, CaO, SrO, and BaO be 0-10% and the total
content (ZrO.sub.2+TiO.sub.2) of ZrO.sub.2 and TiO.sub.2 be
0-5%.
[0083] The individual components of the glass composition will be
described below in detail.
[0084] SiO.sub.2 is not only a component that constitutes the
framework of the glass but also a component for increasing the
chemical durability and for reducing the probability of occurrence
of cracks when a glass surface is scratched. It is preferable that
the content of SiO.sub.2 be 50% or more, even preferably 55% or
more and further preferably 58% or more.
[0085] To increase the meltability of the glass, it is preferable
that the content of SiO.sub.2 be 80% or less, even preferably 75%
or less and further preferably 70% or less.
[0086] Al.sub.2O.sub.3 is not only a component that is effective at
increasing the ion exchangeability at the time of chemical
strengthening and increasing the surface compressive stress after
the strengthening but also a component for increasing the glass
transition temperature (Tg) and the Young's modulus. It is
preferable that the content of Al.sub.2O.sub.3 be 8% or more, even
preferably 10% or more and further preferably 12% or more.
[0087] To increase the meltability, it is preferable that the
content of Al.sub.2O.sub.3 be 20% or less, even preferably 18% or
less and further preferably 15% or less.
[0088] Although B.sub.2O.sub.3 is not indispensable, it may be
added to, for example, increase the meltability at the time of
glass manufacture. Where B.sub.2O.sub.3 is contained, it is
preferable that its content be 0.5% or more, even preferably 1% or
more and further preferably 2% or more.
[0089] To prevent a phenomenon that striae occur at the time of
melting to lower the quality of glass to be subjected to chemically
strengthening treatment, it is preferable that the content of
B.sub.2O.sub.3 be 10% or less, even preferably 8% or less, further
preferably 5% or less, even further preferably 3% or less, and
particularly preferably 1% or less. To increase the acid
resistance, it is preferable that substantially no B.sub.2O.sub.3
be contained.
[0090] In this specification, the expression "substantially no
(substance name) is contained" means that the substance is not
contained except for unavoidable impurity contained in a raw
material etc., that is, the substance is not added intentionally.
More specifically, this expression means that the content of the
substance in the glass base composition is less than 0.1 mol %.
[0091] Li.sub.2O is a component that is necessary to produce
compressive stress to a deep layer of the glass by ion exchange. It
is preferable that Li.sub.2O be contained in the above-mentioned
range.
[0092] Na.sub.2O is a component for forming a surface compressive
stress layer by ion exchange with potassium ions at the time of
chemically strengthening treatment. It is preferable that Na.sub.2O
be contained in the above-mentioned range.
[0093] Although K.sub.2O is not indispensable, it may be added to
increase the glass meltability and suppress occurrence of
devitrification. It is preferable that the content of K.sub.2O be
0.5% or more, even preferably 1% or more and further preferably
1.2% or more.
[0094] To increase the compressive stress produced by ion exchange,
it is preferable that the content of K.sub.2O be 10% or less, even
preferably 9% or less and further preferably 8% or less.
[0095] Each of alkali metal oxides such as Li.sub.2O, Na.sub.2O,
and K.sub.2O is a component for decreasing the glass melting
temperature. It is preferable that the total content
(Li.sub.2O+Na.sub.2O+K.sub.2O) of Li.sub.2O, Na.sub.2O, and
K.sub.2O be 7% or more, even preferably 9% or more, further
preferably 11% or more, and even further preferably 13% or
more.
[0096] To maintain the glass strength, it is preferable that the
total content (Li.sub.2O+Na.sub.2O+K.sub.2O) of Li.sub.2O,
Na.sub.2O, and K.sub.2O be 24% or less, even preferably 20% or
less.
[0097] Whereas each of alkali earth metal oxides such as MgO, CaO,
SrO, and BaO is a component for increasing the glass meltability,
it has a tendency of lowering the ion exchange performance.
[0098] It is therefore preferable that the total content
(MgO+CaO+SrO+BaO) of MgO, CaO, SrO, and BaO be 10% or less, even
preferably 5% or less.
[0099] Where any of MgO, CaO, SrO, and BaO should be contained, it
is preferable that MgO be contained to increase the strength of the
chemically strengthened glass.
[0100] Where MgO is contained, it is preferable that its content be
0.1% or more, even preferably 0.3% or more and further preferably
0.5% or more.
[0101] To enhance the ion exchange performance, it is preferable
that the content of MgO be 10% or less, even preferably 5% or
less.
[0102] Where CaO is contained, it is preferable that its content be
0.1% or more, even preferably 0.2% or more, further preferably 0.5%
or more, and particularly preferably 1% or more.
[0103] From the viewpoint of enhancing the ion exchange
performance, it is preferable that the content of CaO be 5% or
less, even preferably 1% or less. It is further preferable that
substantially no CaO be contained.
[0104] Where SrO is contained, it is preferable that its content be
0.5% or more, even preferably 1% or more.
[0105] To enhance the ion exchange performance, it is preferable
that the content of SrO be 5% or less, even preferably 1% or less.
It is further preferable that substantially no SrO be
contained.
[0106] Where BaO is contained, it is preferable that its content be
0.5% or more, even preferably 1% or more.
[0107] To enhance the ion exchange performance, it is preferable
that the content of BaO be 5% or less, even preferably 1% or less.
It is further preferable that substantially no BaO be
contained.
[0108] ZnO is a component for increasing the glass meltability and
may be contained. Where ZnO is contained, it is preferable that its
content be 0.2% or more, even preferably 0.5% or more.
[0109] To enhance the glass weather resistance, it is preferable
that the content of ZnO be 5% or less, even preferably 1% or less.
It is further preferable that substantially no ZnO be
contained.
[0110] TiO.sub.2 is a component for enhancing the crushability of
the chemically strengthened glass and may be contained. Where
TiO.sub.2 is contained, it is preferable that its content be 0.1%
or more.
[0111] To suppress devitrification at the time of melting, it is
preferable that the content of TiO.sub.2 be 5% or less, even
preferably 1% or less. It is further preferable that substantially
no TiO.sub.2 be contained.
[0112] ZrO.sub.2 is a component for increasing the surface
compressive stress produced by ion exchange and may be contained.
Where ZrO.sub.2 is contained, it is preferable that its content be
0.3% or more, even preferably 0.5% or more, further preferably 0.7%
or more, and even further preferably 1% or more.
[0113] To suppress devitrification at the time of melting, it is
preferable that the content of ZrO.sub.2 be 5% or less, even
preferably 3% or less.
[0114] It is preferable that the total content
(TiO.sub.2+ZrO.sub.2) of TiO.sub.2 and ZrO.sub.2 be 5% or less,
even preferably 3% or less.
[0115] Y.sub.2O.sub.3, La.sub.2O.sub.3, and Nb.sub.2O.sub.5 are
components for enhancing the crushability of the chemically
strengthened glass and may be contained. Where these components are
contained from this point of view, it is preferable that the
content of each of these components be 0.5% or more, even
preferably 1% or more, further preferably 1.5% or more, even
further preferably 2% or more, and particularly preferably 2.5% or
more.
[0116] To make glass devitrification less prone to occur at the
time of melting and thereby prevent quality deterioration of the
chemically strengthened glass, it is preferable that the total
content (Y.sub.2O.sub.3+La.sub.2O.sub.3+Nb.sub.2O.sub.5) of
Y.sub.2O.sub.3, La.sub.2O.sub.3, and Nb.sub.2O.sub.5 be 9% or less,
even preferably 8% or less.
[0117] From the above view point, it is preferable that the content
of each of Y.sub.2O.sub.3, La.sub.2O.sub.3, and Nb.sub.2O.sub.5 be
3% or less, even preferably 2% or less, further preferably 1% or
less, even further preferably 0.7% or less, and particularly
preferably 0.3% or less.
[0118] Small contents of Ta.sub.2O.sub.5 and Gd.sub.2O.sub.3 may be
added to enhance the crushability of the chemically strengthened
glass. To prevent the refractive index and reflectance from
becoming too high, it is preferable that the content of each of
Ta.sub.2O.sub.5 and Gd.sub.2O.sub.3 be 1% or less, even preferably
0.5% or less. It is further preferable that substantially no
Ta.sub.2O.sub.3 and Gd.sub.2O.sub.3 be contained.
[0119] P.sub.2O.sub.5 may be contained to enhance the ion exchange
performance. Where P.sub.2O.sub.5 is contained, it is preferable
that its content be 0.5% or more, even preferably 1% or more.
[0120] To increase the chemical durability, it is preferable that
the content of P.sub.2O.sub.5 be 2% or less. It is even preferable
that substantially no P.sub.2O.sub.5 be contained.
[0121] Where the glass is used in a colored state, a coloring
component may be added in such a content range as not to obstruct
attainment of desired chemical strengthening properties. For
example, preferable coloring components are Co.sub.3O.sub.4,
MnO.sub.2, Fe.sub.2O.sub.3, NiO, CuO, Cr.sub.2O.sub.3,
V.sub.2O.sub.5, Bi.sub.2O.sub.3, SeO.sub.2, TiO.sub.2, CeO.sub.2,
Er.sub.2O.sub.3, and Nd.sub.2O.sub.3. They may be added either
singly or in combination.
[0122] To suppress occurrence of glass devitrification, it is
preferable that the total content of coloring components be 7% or
less, even preferably 5% or less, further preferably 3% or less,
and even further preferably 1% or less. When it is desired to make
the visible light transmittance of the glass high, it is preferable
that substantially none of these coloring components be
contained.
[0123] SO.sub.3, a chloride, a fluoride, or the like may be added
as appropriate as a refining agent at the time of glass melting. It
is preferable that substantially no As.sub.2O.sub.3 be contained.
Where Sb.sub.2O.sub.3 is contained, it is preferable that its
content be 0.3% or less, even preferably 0.1% or less. It is most
preferable that substantially no Sb.sub.2O.sub.3 be contained.
(Low Refractive Index Film)
[0124] The low refractive index film employed in the embodiment is
lower in refractive index than the chemically strengthened
glass.
[0125] There are no particular limitations on the refractive index
nm of the low refractive index film as long as it is lower in
refractive index than the chemically strengthened glass. However,
from the viewpoint of making interference fringes clear, it is
preferable that the refractive index nm be 1.52 or less, even
preferably 1.50 or less, further preferably 1.48 or less, and most
preferably 1.45 or less. On the other hand, from the viewpoint of
preventing a phenomenon that total reflection occurs at the
interface between the chemically strengthened glass and the low
refractive index film and measurement by a surface stress meter is
thereby made difficult, it is preferable that the refractive index
nm be 1.25 or more, even preferably 1.30 or more and further
preferably 1.35 or more.
[0126] From the viewpoint of suppressing expansion of propagation
light, it is preferable that the thickness of the low refractive
index film be 2 nm or more, even preferably 5 nm or more, further
preferably 8 nm or more, even further preferably 10 nm or more, and
particularly preferably 15 nm or more. From the viewpoint of
preventing a phenomenon that total reflection occurs at the
interface between the chemically strengthened glass and the low
refractive index film and stress measurement using a surface stress
meter is thereby made difficult, it is preferable that thickness of
the low refractive index film be 200 nm or less, even preferably
100 nm or less, further preferably 50 nm or less, and even further
preferably 30 nm or less.
[0127] Where the low refractive index film consists of two or more
layers, it is preferable that the total thickness be in the
above-mentioned range.
[0128] The low refractive index film may have one or more functions
selected from the group consisting of an antifouling property,
water repellency, oil repellency, hydrophilicity, and
lipophilicity. A low refractive index film having such a
function(s) is called an "antifouling layer." It is preferable that
the antifouling layer contains a fluorine-based organic
compound.
[0129] Examples of the fluorine-based organic compound are
compounds containing a perfluoroalkyl group and compounds
containing a perfluoropolyether group. It is preferable to use a
silane compound having a perfluoropolyether group.
[0130] An example of the silane compound having a
perfluoropolyether group is a material containing a compound that
is expressed by the following formula (A) and/or its partially
hydrolyzed condensate:
Rf.sup.3-Rf.sup.2-Z.sup.1 (A)
In formula (A), Rf.sup.3 is a group C.sub.mF.sub.2m+1 (m: an
integer selected from 1 to 6) and Rf.sup.2 is a group
--O--(C.sub.aF.sub.2aO).sub.n-- (a: an integer selected from 1 to
6; n: an integer that is larger than or equal to 1). Where n is
larger than or equal to 2, the units --C.sub.aF.sub.2aO-- may be
either the same or different from each other.
[0131] Z.sup.1 is a group
-Q.sup.2-{CH.sub.2CH(SiR.sup.2.sub.qX.sup.2.sub.3-q)}.sub.r--H in
which Q.sup.2 is --(CH.sub.2).sub.s-- (s: an integer selected from
1 to 12) or --(CH.sub.2).sub.s-- containing one or more kinds
selected from an ester linkage, an ether linkage, an amide linkage,
an urethane linkage, and a phenylene group in which all or part of
the units --CH.sub.2-- may be replaced by a unit --CF.sub.2--
and/or a unit --CF(CF.sub.3)--. R.sup.2 is a hydrogen atom or a
monovalent hydrocarbon group in which the number or carbon atoms is
1 to 6 and that may contain a substituent. X.sup.2 is each
independently a hydroxy group or a hydrolyzable group. The
subscript q is an integer selected from 0 to 2, and r is an integer
selected from 1 to 20.
[0132] Examples of the hydrolyzable group as X.sup.2 are an alkoxy
group, an acyloxy group, a ketoxime group, an alkenyloxy group, an
amino group, an aminoxy group, an amide group, an isocyanate group,
and a halogen atom. Among these examples, from the viewpoint of a
balance between stability and ease of hydrolysis, an alkoxy group,
an isocyanate group, and a halogen atom (in particular, chlorine
atom) are preferable. Among various alkoxy groups, alkoxy groups
having the number of carbons of 1 to 3 are preferable and a methoxy
group and an ethoxy group are even preferable.
[0133] For example, "Afluid (registered trademark) S-550" (product
name, produced by AGC Inc.), "KP-801" (product name, produced by
Shin-Etsu Chemical Co., Ltd.), "X-71" (product name, produced by
Shin-Etsu Chemical Co., Ltd.), "KY-130" (product name, produced by
Shin-Etsu Chemical Co., Ltd.), "KY-178" (product name, produced by
Shin-Etsu Chemical Co., Ltd.), "KY-185" (product name, produced by
Shin-Etsu Chemical Co., Ltd.), "KY-195" (product name, produced by
Shin-Etsu Chemical Co., Ltd.), and "Optool (registered trademark)
DSX" (product name, produced by Daikin Industries, Ltd.), which are
on the market, are usable. Materials obtained by adding oil, an
antistatic agent, or the like to materials on the market are also
usable.
[0134] To increase the adhesiveness of the low refractive index
film serving as the antifouling layer to the chemically
strengthened glass, silicon dioxide, alumina, or the like may be
used as an adhesion layer that is another layer of the low
refractive index film. It is preferable that the adhesion layer
have a composition that includes silicon dioxide as a main
component. In this case, it is preferable that the adhesion layer
be formed between the antifouling layer and the chemically
strengthened glass.
[0135] However, as for the low refractive index film serving as the
adhesion layer, the low refractive index film serving as the
adhesion layer may be used singly without being formed together
with the low refractive index film serving as the antifouling
layer.
[0136] The chemically strengthened glass with a film is
particularly useful when used as a cover glass of, for example, a
mobile device such as a cellphone or a smartphone. The chemically
strengthened glass with a film is also useful when used as a cover
glass of a display device not intended for mobile use such as a TV
receiver, a personal computer, or a touch panel. Furthermore, the
chemically strengthened glass with a film is also useful when used
as wall surfaces of an elevator or wall surfaces of a construction
such as a house or a building, that is, an all-surface display. In
addition, the chemically strengthened glass with a film is useful
when used as a construction material such as a window glass, a
table top, or an interior component, for example, of an automobile,
an airplane, or the like as well as a cover glass of each of them,
and a body having a curved surface shape.
<Manufacturing Method of Chemically Strengthened Glass with
Film>
[0137] In the embodiment, glass to be subjected to chemically
strengthening treatment can be manufactured by a known method. For
example, glass having a sheet shape can be manufactured by a method
described below.
[0138] Glass raw materials are mixed together so as to obtain glass
having a desired composition, which is then melted in a glass
melting furnace by heating it. Resulting molten glass is
homogenized by bubbling, stirring, addition of a refining agent,
etc., formed into a glass sheet having a prescribed thickness by a
known forming method, and then cooled gradually. Alternatively, the
molten glass may be formed into a block shape after being
homogenized, cooled gradually, and then cut into a sheet shape.
[0139] Example methods for forming glass having sheet shape are a
float method, a press method, a fusion method, and a down-draw
method. In particular, the float method is preferable for
manufacture of a large-size glass sheet. Continuous forming methods
other than the float method, such as the fusion method and the
down-draw method, are also preferable.
[0140] The resulting glass can be given, for example, the base
composition described in the above section (Chemically strengthened
glass) of <Chemically strengthened glass with film>. The same
can be applied as for a preferable mode.
[0141] The thus-obtained glass is then subjected to chemically
strengthening treatment, whereby chemically strengthened glass is
obtained.
[0142] The chemically strengthening treatment is treatment for
replacing metal ions having a small ion radius in glass with metal
ions having a large ion radius by bringing the glass into contact
with metal salt by, for example, a method of immersing the glass in
a melt of the metal salt containing metal ions having a large ion
radius. Typically, lithium ions are replaced by sodium ions or
potassium ions and sodium ions are replaced by potassium ions.
[0143] To increase the rate of the chemically strengthening
treatment and to cause ion exchange also in a deep layer of glass
to produce stress there, it is preferable to utilize "Li--Na
exchange" which replaces lithium ions in the glass with sodium
ions. To produce large compressive stress at the surface by ion
exchange, it is preferable to utilize "Na--K exchange" which
replaces sodium ions in the glass with potassium ions.
[0144] Example molten salts to be used for the chemically
strengthening treatment are a nitrate, a sulfate, a carbonate, and
a chloride. Among them, example nitrates are lithium nitrate,
sodium nitrate, potassium nitrate, cesium nitrate, and silver
nitrate. Example sulfates are lithium sulfate, sodium sulfate,
potassium sulfate, cesium sulfate, and silver sulfate. Example
carbonates are lithium carbonate, sodium carbonate, and potassium
carbonate. Example chlorides are lithium chloride, sodium chloride,
potassium chloride, cesium chloride, and silver chloride.
[0145] One of these molten salts may be used singly or plural kinds
of molten salts may be used in combination.
[0146] The treatment conditions of the chemically strengthening
treatment such as a time, and a temperature are suitably selected
taking a glass composition, a kind of molten salt, etc. into
consideration. As a result, chemically strengthened glass is
obtained in which two or less interference fringes are observed by
stress measurement utilizing surface propagation light having a
wavelength of 365 nm.
[0147] For example, chemically strengthened glass may be obtained
by the following two-step chemically strengthening treatment.
[0148] As the first-step chemically strengthening treatment, glass
is immersed in a metal salt containing sodium ions, e.g., sodium
nitrate molten salt. The temperature of the metal salt is, for
example, about 350.degree. C. to 500.degree. C., and immersion time
is, for example, about 0.1 to 10 hours. As a result, ion exchange
occurs between lithium ions in the glass and sodium ions in the
metal salt, whereby a compressive stress layer in which, for
example, a surface compressive stress is 200 MPa or more and a
compressive stress layer depth is 80 .mu.m or more is formed.
[0149] If the surface compressive stress obtained by the first-step
treatment is larger than 1,000 MPa, it may be difficult to increase
the compressive stress layer depth (DOL) while keeping the internal
stress (CT) small in chemically strengthened glass obtained
finally. It is therefore preferable that the surface compressive
stress obtained by the first-step treatment be 900 MPa or less,
even preferably 700 MPa or less and further preferably 600 MPa or
less.
[0150] As the second-step chemically strengthening treatment, the
glass that has been subjected to the first-step treatment is
immersed in a metal salt containing potassium ions, e.g., potassium
nitrate molten salt. The temperature of the metal salt is higher
than or equal to the melting temperature of the metal salt. From
the viewpoint of allowing the ion exchange to proceed, it is
preferable that the temperature of the metal salt be 350.degree. C.
or more, even preferably 370.degree. C. or more and further
preferably 390.degree. C. or more. From the viewpoint of allowing
the ion exchange to proceed, it is preferable that the time of
immersion in the metal salt be 10 minutes or more, even preferably
20 minutes or more and further preferably 30 minutes or more.
[0151] On the other hand, from the viewpoint of making the number
of interference fringes observed in stress measurement utilizing
surface propagation light having a wavelength of 365 nm being two
or less, it is preferable that the temperature of the metal salt be
440.degree. C. or less, even preferably 420.degree. C. or less and
further preferably 400.degree. C. or less. From the same point of
view, it is preferable that the time of immersion in the metal salt
be 90 minutes or less, even preferably 70 minutes or less and
further preferably 50 minutes or less.
[0152] One example of chemically strengthening treatment has been
described above. Alternatively, three-step chemically strengthening
treatment may be performed. In each stage of the chemically
strengthening treatment, metal salt may contain plural kinds of
alkali metal ions such as lithium ions and sodium ions, sodium ions
and potassium ions, or lithium ions, sodium ions, and potassium
ions.
[0153] To perform such two-step or three-step chemically
strengthening treatment, from the viewpoint of efficiency of
manufacture, it is preferable that the total treatment time be 10
hours or less, even preferably 5 hours or less and further
preferably 3 hours or less. On the other hand, to obtain a desired
stress profile, it is preferable that the total treatment time be
0.5 hours or more, even preferably 1 hour or more.
[0154] The chemically strengthened glass of the embodiment that is
obtained in the above-described manner may have a shape other than
a sheet shape according to a product, use, or the like to which it
is applied. The chemically strengthened glass may have a chamfered
shape in which outer circumferential portions are different in
thickness. The shape of the chemically strengthened glass is not
limited to these shapes; for example, the two main surfaces need
not always be parallel with each other and all or part of one or
both of the two main surfaces may be a curved surface. More
specifically, for example, the chemically strengthened glass may be
a flat-sheet-shaped glass sheet having no warp or a curved glass
sheet having a curved surface.
[0155] Organic substances sticking to the surfaces may be removed
by immersing the obtained chemically strengthened glass in an
alkali solution. Alternatively, organic substances sticking to the
surfaces may be removed by irradiating the main surfaces of the
chemically strengthened glass with plasma in the atmosphere.
[0156] Removal of organic substances sticking to the surfaces is
preferable because it increases the adhesiveness to a film formed
on a main surface and thereby increases the durability.
[0157] A low refractive index film is formed on a main surface of
the chemically strengthened glass. The method for forming a low
refractive index film varies depending on the kind of film to be
formed.
[0158] Where the low refractive index film is an adhesion film for
increasing the adhesiveness, a film can be formed by a chemical
vapor deposition (CVD) method or a physical vapor deposition (PVD)
method. Examples of the physical vapor deposition method are a
vacuum deposition method, an ion-assisted sputtering (IAD) method,
a sputtering method, a post-oxidation sputtering method, an
ion-assisted sputtering method, an ion beam sputtering method, and
an ion-beam-assisted deposition method. Among these methods, the
ion-assisted sputtering method, the post-oxidation sputtering
method, and the ion-beam-assisted deposition method are preferable
in that the hardness of an adhesion layer can be increased
relatively easily.
[0159] From the viewpoint of increasing the hardness of an adhesion
layer, it is preferable that the pressure in a chamber at the time
of vacuum deposition be 0.15 Pa or less, even preferably 0.1 Pa or
less and further preferably 0.08 Pa or less. From the viewpoint of
maintaining plasma discharge stably, it is preferable that the
pressure be 0.03 Pa or more.
[0160] It is preferable that the material for the vacuum deposition
to form an adhesion layer be silicon dioxide (SiO.sub.2). The
material is set in a heating container and evaporated by heating it
under a low vacuum, whereby a film is formed on a main surface of
glass that is set to be opposed to the heating container.
[0161] Where the sputtering method is employed, from the viewpoint
of increasing the hardness of a film, it is preferable that the
discharge power at the time of film formation be 5,000 W or more,
even preferably 7,000 W or more. From the viewpoint of preventing
cracking of a target and abnormal discharge, it is preferable that
the discharge power be 20,000 W or less.
[0162] During the formation of an adhesion film, it is preferable
that the adhesion film is exposed to high energy particles from a
plasma source, an ion source, or a radical source, or the like,
that is, plasma assistance is performed. It is preferable that
plasma assistance be performed every time when a film of 100 nm or
thinner is formed, even preferably every time when a film of 1 nm
or thinner is formed and further preferably every time when a film
of 0.5 nm or thinner is formed.
[0163] Although there are no particular limitations on the type of
a high-energy particle source, it is preferable to use an ion beam,
a radical source, an ECR (electron cyclotron resonance) plasma
source or the like, such as a plasma beam, an ion beam, a linear
ion beam, an ECR plasma source, a radical source, or a
low-impedance antenna plasma source.
[0164] It is preferable to execute the above process using, for
example, a sputtering machine (e.g., "RAS1100B II" produced by
Shincron Co., Ltd.) capable of performing a post-oxidation
sputtering method.
[0165] In the case of forming an SiO.sub.2 film as an adhesion
layer, it is preferable to employ an Si target, to use argon gas
and oxygen gas as discharge gas in a film forming chamber, and to
use argon and oxygen as discharge gas in a reaction chamber. In the
above-mentioned machine, a drum that holds a substrate is set in a
vacuum chamber that is divided into a film forming chamber and a
reaction chamber and rotated at, for example, 100 rpm while passing
through the film forming chamber and the reaction chamber
alternately at high speed. As a result, a thin film that is as very
thin as several nanometers or less is formed in the film forming
chamber. Subsequently, activated gas that has reacted with a plasma
source energy may be used to apply energy to the film that has been
sent to the reaction chamber or to react with portions of the film
which has not reacted yet.
[0166] To increase the hardness of an adhesion layer, it is
preferable to use such a machine capable of performing
post-oxidation process. Furthermore, it is preferable to apply
energy to an SiO.sub.2 film by using the plasma source in the
reaction chamber after the SiO.sub.2 film which has been
sufficiently oxidized has been formed in the film forming
chamber.
[0167] In the case where a low refractive index film is an
antifouling layer having one or more functions selected from the
group consisting of an antifouling property, water repellency, oil
repellency, hydrophilicity, and lipophilicity, a wet method such as
a spin coating method, a dip coating method, a casting method, a
slit coating method, or a spray coating method or a dry method such
as a vacuum deposition method is used.
[0168] To form an antifouling layer that is high in adhesion and
wear resistance, it is preferable to employ a vacuum deposition
method. Examples of the vacuum deposition method are a resistance
heating method, an electron beam heating method, a high-frequency
induction heating method, a reactive deposition method, a molecular
beam epitaxy method, a hot wall deposition method, an ion plating
method, and a cluster ion beam method. Among these methods, the
resistance heating method is preferable because a machine used is
simple and hence the cost is low.
[0169] An antifouling layer may be formed on a main surface of
chemically strengthened glass either directly or via another layer
such as an adhesion layer.
[0170] From the viewpoint of performing vacuum deposition without
causing any problem, it is preferable that the pressure in the
chamber at the time of the vacuum deposition be 5.times.10.sup.-3
Pa or less. From the viewpoint of keeping deposition rate of the
antifouling layer at a prescribed rate or more, it is preferable
that the pressure in the chamber at the time of the vacuum
deposition be 1.times.10.sup.-4 Pa or more.
[0171] From the viewpoint of preventing water absorption on an
antifouling layer and thereby forming the film stably, it is
preferable that the deposition power as converted into a current
density be 200 kA/m.sup.2 or more, even preferably 300 kA/m.sup.2
or more and further preferably 350 kA/m.sup.2 or more. From the
viewpoint of preventing evaporation of components of steel wool
impregnated with a material of an antifouling layer and components
of a crucible, it is preferable that the deposition power be 1,000
kA/m.sup.2 or less.
[0172] It is preferable that a deposition material be held in such
a manner that a fluorine-based organic compound to constitute an
antifouling layer is impregnated in a pellet-shaped copper
container. It is preferable to perform impregnation work in a
nitrogen atmosphere. This increases the number of layers in which a
fluorine-based organic compound is deposited as monoatomic
molecules is increased, whereby a resulting antifouling layer is
increased in wear resistance.
[0173] In the case where the low refractive index film is an
antireflection on layer, for example, it can be formed by a
chemical vapor deposition (CVD) method or a physical vapor
deposition (PVD) method. Examples of the physical vapor deposition
method are a vacuum deposition method and a sputtering method.
<Surface Stress Measuring Method>
[0174] The measurement target of the surface stress measuring
method of the embodiment is a chemically strengthened glass having
two or less interference fringes observed under stress measurement
that utilizes surface propagation light having a wavelength of 365
nm. The chemically strengthened glass has a pair of main surfaces
opposing each other.
[0175] When the chemically strengthened glass alone is subjected to
stress measurement utilizing surface propagation light having a
wavelength of 365 nm, the number of interference fringes observed
is two or less and the interference fringes are unclear because of
a small stress depth, and thus the measurement of surface
compressive stress is difficult or impossible.
[0176] However, in the case where a chemically strengthened glass
with a film in which at least one main surface of chemically
strengthened glass is formed with a film that is lower in
refractive index than the chemically strengthened glass is used,
clear interference fringes are obtained and surface compressive
stress can be measured easily.
[0177] That is, the surface stress measuring method of the
embodiment includes the following steps (1) and (2):
[0178] (1) A step of obtaining a chemically strengthened glass with
a film by forming a film (low refractive index film) that is lower
in refractive index than the chemically strengthened glass on at
least one of main surfaces of the chemically strengthened glass
having two or less interference fringes observed under stress
measurement utilizing surface propagation light having a wavelength
of 365 nm.
[0179] (2) A step of measuring surface compressive stress of the
chemically strengthened glass by performing stress measurement
utilizing surface propagation light on the obtained chemically
strengthened glass with a film.
[0180] It becomes possible to observe interference fringes clearly
in stress measurement utilizing surface propagation light by
forming a low refractive index film on a main surface of the
chemically strengthened glass.
[0181] Observed interference fringes become clearer and the number
thereof is increased as the wavelength of surface propagation light
becomes shorter. The wavelength for stress measurement is not
limited to 365 nm and may be another wavelength such as 596 nm or
790 nm. From the viewpoint of making it easier to observe clear
interference fringes, it is preferable that the wavelength of
surface propagation light be 650 nm or less, even preferably 550 nm
or less. Where "FSM-6000LEUV" produced by Orihara Industrial Co.,
Ltd. is used as a glass surface stress meter of Orihara Industrial
Co., Ltd., the lower limit of the wavelength is 365 nm. However, if
measurement at an even shorter wavelength range is possible,
surface propagation light having wavelength lower than 365 nm may
be used. Furthermore, measurement may be carried out using plural
wavelengths.
EXAMPLES
[0182] Although Examples of the present invention will be described
below, the invention is not restricted by these Examples.
[0183] Examples 1 and 6-19 are Referential Examples, Example 2 is a
Comparative Example, and Examples 3-5 are Inventive Examples.
(Measuring Method)
[0184] Surface compressive stress and a surface stress depth of
chemically strengthened glass were measured by a glass surface
stress meter ("FSM-6000LEUV" produced by Orihara Industrial Co.,
Ltd.). The wavelength of a light source of surface propagation
light was 365 nm.
[0185] A stress depth of a deep layer and tensile stress in a glass
central portion of the chemically strengthened glass were measured
by a scattered light photoelastic stress meter ("SLP2000" produced
by Orihara Industrial Co., Ltd.).
[0186] A refractive index of the chemically strengthened glass was
measured by a Kalnew precision refractive index meter "KPR-2000"
produced by Shimadzu Corporation. As for a refractive index of a
low refractive index film, a value calculated according to
conventional knowledge was used.
Example 1
[0187] Glass raw materials were mixed so as to obtain each of
compositions shown in Table 1 in mole percentage on an oxide basis,
and were subjected to heat melting. Resulting molten glass was then
homogenized and cooled gradually. Resulting glass was formed and
processed into a glass sheet of 50 mm.times.50 mm having a
thickness t of 0.70 mm. Blanks in Table 1 mean that the
corresponding materials are not contained except for impurities
that are contained in the raw materials unavoidably, that is, they
are not contained intentionally.
[0188] The glass sheet obtained was subjected to first-step
chemically strengthening treatment by immersing it in NaNO.sub.3
molten salt of 380.degree. C. for 150 minutes. Then the glass sheet
was subjected to second-step chemically strengthening treatment by
immersing it in KNO.sub.3 molten salt of 450.degree. C. for 60
minutes, whereby chemically strengthened glass was obtained.
[0189] The chemically strengthened glass obtained was subjected to
measurement of surface compressive stress, a surface stress depth,
a stress depth of a deep layer, and tensile stress.
[0190] FIG. 1 shows an image obtained by measurement using a
surface stress meter. The upper half of FIG. 1 is an image obtained
by measurement using P-polarized light in which six clear
interference fringes were observed. The lower half of FIG. 1 is an
image obtained by measurement using S-polarized light in which five
clear interference fringes were observed.
[0191] This chemically strengthened glass had a surface compressive
stress of 990 MPa, a surface stress depth of 7.5 .mu.m, a deep
layer stress depth of 127 .mu.m, and a tensile stress of 84
MPa.
[Table 1]
TABLE-US-00001 [0192] TABLE 1 Ex. 1 to Ex. Ex. Ex. Ex. Ex. Ex. Ex.
Ex. Ex. Ex. Ex. Ex. Ex. Ex. (mol %) Ex. 5 6 7 8 9 10 11 12 13 14 15
16 17 18 19 SiO.sub.2 69 68.9 68.9 68.9 68.8 68.8 68.5 67.6 66.4
64.3 65.7 66.5 67.8 66.4 66.5 Al.sub.2O.sub.3 13 12.4 12.0 12.2
12.0 12.0 12.0 13.0 12.4 12.4 13.0 13.0 12.4 12.2 12.0 MgO 0.1 0.3
0.3 0.1 0.3 0.3 0.1 3.0 5.0 3.0 3.0 0.6 2.0 3.0 CaO 0.1 0.1 0.1 0.2
0.2 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 TiO.sub.2 0.1 0.1 0.1 0.1
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 ZrO.sub.2 0.3 0.3 0.3 0.7
0.5 1.0 0.3 0.3 0.3 0.3 0.3 0.5 0.5 0.9 Y.sub.2O.sub.3 1 1.3 1.5
1.3 1.3 1.3 1.1 1.3 1.3 1.3 1.3 1.3 2.0 2.0 0.9 Li.sub.2O 11 10.8
10.8 10.8 10.8 10.8 10.8 11.0 10.6 10.6 10.6 10.6 10.6 10.6 10.6
Na.sub.2O 5 4.8 4.8 4.8 4.8 4.8 4.8 4.7 4.7 3.9 4.7 3.2 4.7 4.9 4.7
K.sub.2O 1 1.2 1.2 1.2 1.2 1.2 1.2 1.8 1.2 2.0 1.2 2.0 1.2 1.2 1.2
Total 100 100 100 100 100 100 100 100 100 100 100 100 100 100
100
Example 2
[0193] A glass sheet was obtained in the same manner as in Example
1 except that the glass thickness t was 0.75 mm.
[0194] The glass sheet obtained was subjected to first-step
chemically strengthening treatment by immersing it in NaNO.sub.3
molten salt of 380.degree. C. for 140 minutes. Then the glass sheet
was subjected to second-step chemically strengthening treatment by
immersing it in KNO.sub.3 molten salt of 390.degree. C. for 50
minutes, whereby chemically strengthened glass was obtained.
[0195] The chemically strengthened glass obtained was subjected to
measurement of a surface compressive stress, a surface stress
depth, a stress depth of a deep layer, and a tensile stress.
[0196] FIG. 2 shows an image obtained by measurement using the
surface stress meter. The upper half of FIG. 2 is an image obtained
by measurement using P-polarized light in which two unclear
interference fringes were observed. The lower half of FIG. 2 is an
image obtained by measurement using S-polarized light in which two
unclear interference fringes were observed. In either case, neither
a surface compressive stress nor a surface stress depth was
determined by automatic measurement using the surface stress meter.
Thus, a surface compressive stress and a surface stress depth were
determined by visually determining positions of the interference
fringes in the image of FIG. 2.
[0197] This chemically strengthened glass had a surface compressive
stress of 1,220 MPa, a surface stress depth of 2.9 .mu.m, a deep
layer stress depth of 106 .mu.m, and a tensile stress of 65
MPa.
Example 3
[0198] Chemically strengthened glass was obtained in the same
manner as in Example 2. The chemically strengthened glass obtained
was cleaned by immersing it in pure water and an alkaline
detergent. Then plasma cleaning was performed by irradiating a main
surface, located on the side for film formation, of the chemically
strengthened glass with plasma.
[0199] Subsequently, a low refractive index film A was formed on
the main surface of the chemically strengthened glass by a vacuum
deposition method with resistance heating using a fluorine-based
organic compound ("UD-509" produced by Daikin Industries, Ltd.) as
a material, whereby a chemically strengthened glass with a film was
obtained. This was done in such a manner that material liquid was
impregnated in steel wool provided in a pellet-shaped copper
container in a nitrogen atmosphere and the material was supported
by the container by evacuation. The low refractive index film A was
formed by depositing the material for 300 sec at deposition power
of 318.5 kA/m.sup.2 with the pressure in the vacuum chamber set at
3.0.times.10.sup.-3 Pa. The low refractive index film A formed had
a thickness of 15 nm.
[0200] Whereas the refractive index of the chemically strengthened
glass was 1.54 at a wavelength of 365 nm and 1.52 at a wavelength
of 589 nm, the refractive index of the low refractive index film A
was in a range of 1.40 to 1.42 at a wavelength of 589 nm. That is,
the difference between the refractive indices of the low refractive
index film A and the chemically strengthened glass was 0.10 to
0.12.
[0201] FIG. 3 shows an image obtained by measurement using the
surface stress meter. The upper half of FIG. 3 is an image obtained
by measurement using P-polarized light and the lower half of FIG. 3
is an image obtained by measurement using S-polarized light. In
either case, in contrast to the case of Example 2 in which the low
refractive index film A was not formed, clear interference fringes
were observed and hence automatic measurement using the surface
stress meter was possible.
[0202] This chemically strengthened glass had a surface compressive
stress of 1,220 MPa, a surface stress depth of 2.9 .mu.m, a deep
layer stress depth of 106 .mu.m, and a tensile stress of 65
MPa.
Example 4
[0203] Chemically strengthened glass was obtained in the same
manner as in Example 2. The chemically strengthened glass obtained
was cleaned by immersing it in pure water and an alkaline
detergent. Then plasma cleaning was performed by irradiating a main
surface, located on the side for film formation, of the chemically
strengthened glass with plasma.
[0204] Subsequently, a low refractive index film B was formed on
the main surface of the chemically strengthened glass by a
sputtering method. A sputtering machine "RAS1100B II" produced by
Shincron Co., Ltd. was used. The low refractive index film B was an
SiO.sub.2 film and polycrystalline silicon (produced by Chemiston
Inc., purity 5N) was used as a sputtering target. After checking
that the pressure in a film forming chamber became
5.times.10.sup.-5 Pa or less, argon was introduced into the film
forming chamber at 80 sccm as discharge gas and electric power of
7,500 W was applied to the sputtering target. Subsequently, oxygen
was introduced into the reaction chamber at 110 sccm, and then
discharging was performed with the electric power of an RF plasma
source set at 3,000 W. Under the above conditions, the low
refractive index film B was formed at a thickness of 5 nm.
[0205] Furthermore, a low refractive index film A was formed on the
low refractive index film B in the same manner as in Example 3,
whereby a chemically strengthened glass with a film was obtained.
The thickness of the low refractive index film A was 15 nm.
[0206] Whereas the refractive index of the chemically strengthened
glass was 1.54 at a wavelength of 365 nm and 1.52 at a wavelength
of 589 nm, the refractive index of the low refractive index film A
was in a range of 1.40 to 1.42 at a wavelength of 589 nm. That is,
the difference between the refractive indices of the low refractive
index film A and the chemically strengthened glass was 0.10 to
0.12. The refractive index of the low refractive index film B was
1.49 at a wavelength of 365 nm and 1.47 at a wavelength of 589 nm.
That is, the difference between the refractive indices of the low
refractive index film B and the chemically strengthened glass was
0.05.
[0207] FIG. 4 shows an image obtained by measurement using the
surface stress meter. The upper half of FIG. 4 is an image obtained
by measurement using P-polarized light and the lower half of FIG. 4
is an image obtained by measurement using S-polarized light. In
either case, in contrast to the case of Example 2 in which neither
the low refractive index film A nor the low refractive index film B
was formed, clear interference fringes were observed and hence
automatic measurement using the surface stress meter was
possible.
[0208] This chemically strengthened glass had a surface compressive
stress of 1,240 MPa, a surface stress depth of 2.9 .mu.m, a deep
layer stress depth of 106 .mu.m, and a tensile stress of 65
MPa.
Example 5
[0209] Chemically strengthened glass with a film was obtained in
the same manner as in Example 4 except that the thickness of a low
refractive index film B was 10 nm. Film forming conditions of the
low refractive index film B were as follows.
[0210] Argon was introduced into the film forming chamber at 80
sccm as discharge gas and electric power of 7,500 W was applied to
a sputtering target. Subsequently, oxygen was introduced into the
reaction chamber at 110 sccm, and then discharging was performed
with the electric power of an RF plasma source set at 3,000 W.
Under these conditions, a low refractive index film was formed at a
thickness of 10 nm.
[0211] Whereas the refractive index of the chemically strengthened
glass was 1.54 at a wavelength of 365 nm and 1.52 at a wavelength
of 589 nm, the refractive index of the low refractive index film A
was in a range of 1.40 to 1.42 at a wavelength of 589 nm. That is,
the difference between the refractive indices of the low refractive
index film A and the chemically strengthened glass was 0.10 to
0.12. The refractive index of the low refractive index film B was
1.49 at a wavelength of 365 nm and 1.47 at a wavelength of 589 nm.
That is, the difference between the refractive indices of the low
refractive index film B and the chemically strengthened glass was
0.05.
[0212] FIG. 5 shows an image obtained by measurement using the
surface stress meter. The upper half of FIG. 5 is an image obtained
by measurement using P-polarized light and the lower half of FIG. 5
is an image obtained by measurement using S-polarized light. In
either case, in contrast to the case of Example 2 in which neither
the low refractive index film A nor the low refractive index film B
was formed, clear interference fringes were observed and hence
automatic measurement using the surface stress meter was
possible.
[0213] This chemically strengthened glass had a surface compressive
stress of 1,240 MPa, a surface stress depth of 2.9 .mu.m, a deep
layer stress depth of 106 .mu.m, and a tensile stress of 65
MPa.
Examples 6-19
[0214] Chemically strengthened glass of each of Examples 6-19 was
obtained in the same manner as in Example 1 except that glass raw
materials were mixed so that a composition shown in Table 1 in mole
percentage on an oxide basis was obtained.
[0215] It was found from the above results that if the depth of
surface stress produced by ion exchange between potassium ions and
sodium ions was small, interference fringes obtained by surface
stress measurement became unclear and the number thereof decreased,
as a result of which neither a surface compressive stress nor a
surface stress depth was determined by automatic measurement using
a surface stress meter.
[0216] In contrast, in the case where a low refractive index film
was formed on a main surface of chemically strengthened glass,
interference fringes became clear and it became possible to measure
a surface compressive stress and a surface stress depth by
automatic measurement.
[0217] The present invention is described in detail with reference
to specific embodiments, but it is apparent for those skilled in
the art that various changes or modifications can be added without
departing from the spirit and the scope of the present invention.
This application is based upon Japanese Patent Application (No.
2020-151342), filed on Sep. 9, 2020, the contents of which are
incorporated herein by reference.
* * * * *